1. Field of the Invention
The present invention generally relates to pressure vessels and, more particularly, to air relief valves for such vessels.
2. Description of the Related Art
During the development of pressure vessels, it has become common to include valves which release air during filling of the vessel with liquid. Over the years, these valves have been developed to automatically bleed air from the pressure vessel until the water therein reaches a predetermined level, at which point the valve automatically prevents the further escape of air.
U.S. Pat. No. 3,786,829, which issued on Jan. 22, 1974, discloses a common type of pressure vessel air relief valve. The '829 patent includes a downwardly directed tube which extends between the interior of the pressure vessel and an inner chamber of the valve body. The chamber, which is located intermediate the tube and a vent, is provided with a float ball which operates to seal the vent when the water in the pressure vessel reaches a predetermined level. During filling of the pressure vessel, air is allowed to escape from the vessel by way of the tube, chamber, and vent. A flow diverting plate positioned under the ball permits escaping air to rise around the ball without causing the ball to prematurely seal the vent. When the water reaches a predetermined level, air from the vessel is no longer admitted to the tube. Thereafter, the addition of further water into the pressure vessel causes water to flow into the chamber via the tube, forcing the float ball to rise and sealingly engage the upper end of the chamber. There is no provision for a manual air valve to bleed or introduce air into the inner chamber of the valve body to facilitate draining of the system.
The automatic air relief valves known in the art generally operate under the principle that a certain amount of air should remain in the pressure vessel during operation of the system to encourage pressure build-up therein. However, such air is undesirable in many applications, such as swimming pool filter systems. In such systems, it is most desirable that substantially all of the air is removed from the system prior to operation thereof. Also, the air valves known in the art generally do not include a manual air valve to introduce air into the system to aid in draining thereof. Furthermore, the known systems are generally unsatisfactory when the system is operated at low pressure due to leakage of air or Water around the float valve.